Wasim did under-achieve. He should have ended up with over 500 test wickets given his talent.
The reason his career stats dont measure up to his peers is that he had a slower than usual start to his career from 85 to 90 before he became world class, and a slow dip at the end when he lost much of his penetration.
If we evaluated his stats just from the 90s decade, when he was at his peak, it lines up well with his contemporaries.
Cricket Records | Records | 1990s | Test matches | Most wickets | ESPN Cricinfo
If I had to pick a bowler of the 90s, I would be split between Wasim and Ambrose. Here's a list of top class cricketers I know who have rated Wasim as either best or joint best, just from the top of my head:
McGrath, Donald, Atherton, Ambrose, Walsh, Michael Slater, Kapil Dev, Stephen Fleming, Kallis, Ganguly, Mark Taylor, Ricky Ponting, Brian Lara, Chris Cairns, and so on.
In the final summary though, I think Wasim suffers in comparison to the elites such as Ambrose, Lillee, Hadlee, Imran, Marshall and McGrath as never quite ran through sides with regularity the way they did. Batsmen often found him so awkward a proposition and focused on just playing him out. A lot of wickets would fall from the other end. Also, Wasim wasnt the best bowler at thinking the batsman out, by his own admission he often didnt know what ball would be coming next. I say this as one of his biggest fans though.
In the end, Wasim's name certainly belongs with the best of the best, based mostly on peer rating, but I would hesitate to put him near the top.